1. Field of The Invention
The present invention relates to the field of air pollution control. More particularly, the present invention relates to the field of an air pollution control process which is intended to be used primarily for nitric oxide (NO.sub.x) emissions reduction and post combustion gases at power plants and industrial boilers.
2. Description of The Prior Art
There has been considerable effort put forth in recent years to solving environmental and ecological problems, such as unhealthful air quality, acid rain, etc. Fuel combustion is the main source of air pollutants discharged into the atmosphere. Unless combustion exhaust gases are treated to remove deleterious air pollutants, the degradation of the environment will continue. One of the most prevalent components in polluted air are nitrogen oxides (NO.sub.x). A major NO.sub.x component is nitric oxide (NO) which is the primary pollutant in all fuel combustion exhaust gases. Nitric oxide gas oxidizes in the atmosphere to form nitrogen dioxide (NO.sub.2). Nitrogen dioxide is the primary reactant in atmospheric, photochemical reactions which produce unhealthful air pollutants, such as ozone. Nitrogen dioxide is also known to be an acid gas which, together with sulfur dioxide, causes acid rain.
Major sources of NO emissions are internal combustion engines and utility boilers. Nitric oxide is formed at high temperatures during fuel combustion by (1) the reaction of nitrogen and oxygen gas components of combustion air (thermal NO.sub.x), and (2) the oxidation of fuel-bound nitrogen compounds (fuel NO.sub.x). It is estimated that mobile sources, such as automobiles, trucks, and buses produce about 40% to about 50% of nitrogen oxides emissions in this country, while utility boilers produce about 33%.
Various methods are used to reduce nitrogen oxides in combustion exhaust gases so that gases may be discharged without harm to public health and the environment. Nitrogen oxides emissions from internal combustion engines and boilers are reduced by lowering peak combustion temperatures. Operational adjustments of air/fuel stoichiometry and mixing techniques and design modifications of engine and boiler components are used to lower NO.sub.x emissions.
Post combustion utility boiler NO.sub.x emissions control methods are described in "NOx Control Technologies and Their Availability and Extent of Application" (USEPA), February 1992, EPA-450/3-92-004. Several methods involve use of various chemicals, such as ammonia, urea, and cyanuric acid to reduce the nitrogen oxide content of exhaust gases by converting the nitrogen oxides to innocuous gases. Such chemical injection and reaction methods are commonly known as selective non-catalytic reduction (hereafter referred as "SNR"). SNR generally requires extremely high temperatures such as in the range of about 1600.degree. F. and higher. SNR chemical reactions are slow, highly temperature sensitive, and sensitive to real-distribution of chemicals in the reaction zone. SNR generally require excess of chemicals in the reaction zone which tend to pass through the reaction zone and become secondary air pollutants. At its high operating temperature, SNR using ammonia or urea reduce NO.sub.x emissions by about 40%.
Slow, SNR chemical reactions for reducing nitrogen oxides content in exhaust gases are accelerated by use of catalysts effective in promoting the reduction of nitrogen oxides above 600.degree. F. Methods using catalysts are generally referred to as selective catalytic reduction (hereafter referred to as "SCR"). Using catalysts with ammonia or urea injection in exhaust gas streams offers about 80% NO.sub.x emissions reduction but has a number of disadvantages. Disadvantages are high cost of catalyst, retrofit installation due to modifications required of boiler ducting, combustion air fans, heat transfer surfaces, and control system. SCR has limited ability to follow load changes while maintaining minimal ammonia pass-through due to reaction temperature sensitivity. Its application is generally limited to boilers not subject to frequent load changes. Catalyst replacement due to catalyst fouling and aging occurs about every three to five years resulting in boiler downtime and catalyst replacement costs.
In general, according to "NO.sub.x Control Technologies and Their Availability and Extent of Application" (USEPA), February 1992, the availability of post combustion NO.sub.x emission control methods is limited. As a result, no prior art exists for the application of scientific findings regarding use of deactivated nitrogen for post combustion NO.sub.x reduction or of any nitrogen oxides emissions control methods.
The following ten (10) prior art patents were uncovered in the pertinent field of the present invention:
1. U.S. Pat. No. 3,315,476 issued to Kortlandt et al. on Apr. 25, 1967 for "Controlled Nitrogen Addition To Recovered Hydrogen" (hereafter "the Kortlandt Patent"); PA1 2. U.S. Pat. No. 3,531,664 issued to Hals on Sep. 29, 1970 for "Means For And Method Of Removing Pollutants From Products of Combustion" (hereafter "the Hals Patent"); PA1 3. U.S. Pat. No. 4,235,704 issued to Luckenbach on Nov. 25, 1980 for "Method Of Reducing Oxides Of Nitrogen Concentration In Regeneration Zone Flue Gas" (hereafter "the Luckenbach Patent"); PA1 4. U.S. Pat. No. 4,863,705 issued to Epperly et al. on Sep. 5, 1989 for "Process For The Reduction Of Nitrogen Oxides In An Effluent" (hereafter "the Epperly Patent"); PA1 5. U.S. Pat. No. 4,921,683 issued to Bedell on May 1, 1990 for "Nitric Oxide Abatement Chelates" (hereafter "the Bedell Patent"); PA1 6. U.S. Pat. No. 5,171,554 issued to Gardner-Chavis et al. on Dec. 15, 1992 for "Conversion Of Formaldehyde And Nitrogen To A Gaseous Product And Use Of Gaseous Product In Reduction Of Nitrogen Oxide In Effluent Gases" (hereafter "the '554 Gardner-Chavis Patent"); PA1 7. U.S. Pat. No. 5,234,670 issued to Gardner-Chavis et al. on Aug. 10, 1993 for "Reduction Of Nitrogen Oxide In Effluent Gases Using NCO Radicals (hereafter "the '670 Gardner-Chavis Patent"); PA1 8. U.S. Pat. No. 5,260,043 issued to Li et al. on Nov. 9, 1993 for "Catalytic Reduction Of NOx And Carbon Monoxide Using Methane In The Presence Of Oxygen" (hereafter "the Li Patent"); PA1 9. U.S. Pat. No. 5,286,467 issued to Sun et al. on Feb. 15, 1994 for "Highly Efficient Hybrid Process For Nitrogen Oxides Reduction (hereafter "the Sun Patent"); and PA1 10. U.S. Pat. No. 5,372,706 issued to Buchanan et al. on Dec. 13, 1994 for "FCC Regeneration Process With Low NO.sub.x CO Boiler" (hereafter "the Buchanan Patent").
The Kortlandt Patent discloses a method related to the controlled nitrogen addition to recovered hydrogen responsive to temperature.
The Hals Patent discloses a method and apparatus for NO.sub.x reduction, which involves the use of sulfuric acid.
The Luckenbach Patent discloses a method of reducing NO.sub.x concentration in exit flue gas in the regeneration zone of a catalytic cracking unit. It controls the NO.sub.x concentration in the exit flue gas by adjusting the concentration of combustion promotor, which may be gold, silver, platinum, palladium, iridium, rhodium, mercury, ruthenium, osmium or rhenium.
The Epperly Patent discloses a method of NO.sub.x reduction in combustion effluent. The method involves introducing into the effluent a treatment agent comprising a five or six member heterocyclic hydrocarbons having at least one cyclic nitrogen.
The Bedell Patent discloses an NO abatement process for treatment of NO containing fluid. The process utilizes a polymeric cobalt (II) dioxygen diamine complex for contact with the NO containing stream.
The '554 and '670 Gardner-Chavis Patents disclose a method for the reduction of NO.sub.x in effluent gases by using NCO radicals. One method of obtaining the NCO radicals is by passing cyanuric acid through a catalytic decomposition zone. Another method, as introduced in the '554 Gardner-Chavis Patent and also disclosed in the '670 Gardner-Chavis Patent, is by passing formaldehyde (methanal) H.sub.2 CO and nitrogen or nitric oxide through a catalyst reactor. The catalyst reactor comprises Vanadium (V), Zirconium (Zr) or their mixture.
The Li Patent discloses a process of catalytically reducing NO.sub.x and CO in combustion effluent. The process involves the step of introducing methane into the effluent, and reacting the mixture with a crystalline zeolite which is exchanged with a cation selected from the group consisting of gallium, niobium, cobalt, nickel, iron, chromium, rhodium and manganese.
The Sun Patent discloses a hybrid process for NO.sub.x reduction. It involves the steps of first introducing a nitrogenous treatment agent such as urea into the effluent, then introducing ammonia into the effluent, and finally contacting the treated effluent with a NO.sub.x reducing catalyst. The catalyst may comprise vanadium oxide, tungsten oxide, titanium oxide, iron oxide, copper oxide, manganese oxide, chromium oxide, and noble metals such as the platinum group metals (e.g., platinum, palladium, rhodium and iridium) or their mixtures.
The Buchanan Patent discloses a fluidized catalytic cracking (FCC) regeneration process with low NO.sub.x CO boiler. The process involves operating the FCC regenerator in partial CO bun mode and adding air to the flue gas.
There exists a present need for a process which can achieve maximum NO.sub.x reduction in the post combustion stage (e.g., boiler convection section, flue gas duct or the stack) and utilizing a catalyst to produce a desired agent for that purpose. The catalyst will deactivate the nitrogen atom so that it is ready to rapidly react with NO.sub.x and not produce deleterious by product pollutants.